System And Method For Artifact Reduction In An Image

ABSTRACT

Selected artifacts, which may be based on distortions or selected attenuation features, may be reduced or removed from a reconstructed image. Various artifacts may occur due to the presence of a metal object in a field of view. The metal object may be identified and removed from a data that is used to generate a reconstruction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/375,292, filed on Apr. 4, 2019, which claims the benefit of U.S.Provisional Application No. 62/654,038, filed on Apr. 6, 2018. Theentire disclosure of the above applications are incorporated herein byreference.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under R01-EB-017226awarded by National Institutes of Health. The government has certainrights in the invention.

FIELD

The subject disclosure relates to displaying an image, and particularlyto correction or reduction of artifacts or distortion.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

When acquiring image data or images of a selected object, such as ahuman patient, various artifacts or distortions may occur. For example,when acquiring X-ray based images of a subject, certain materials mayinterfere with X-rays in a manner disproportionate or different thanother materials, such as tissue of a subject. For example, metal orpolymer objects may attenuate and/or scatter X-rays in a mannerdifferent from the surrounding tissue of the subject. These effects ofthe non-tissue material may cause distortion or artifacts in the imagesgenerated with the acquired image data. The distortions may be amplifiedor easily viewed after a reconstruction, such as a three-dimensionalreconstruction, based upon the two-dimensional projections of thesubject. Correction of the distortions, therefore, may be selected in anattempt to generate images for viewing that are minimally distorted orwithout distortion.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A subject may be imaged with a selected imaging system. In variousembodiments, an X-ray imaging system may be used to acquire image dataof the subject. The X-ray image data may be acquired according tovarious techniques, such as with an X-ray system that creates oracquires one or more two-dimensional projections. The two-dimensionalprojections may be used to generate a three-dimensional reconstruction.Accordingly, one or more two-dimensional projections may be acquired,such as in a sequence, to generate the three-dimensional reconstruction.

In acquiring the image data of the subject, the X-rays are attenuated bythe material through which the X-rays pass from an X-ray source to adetector. The X-rays emitted from a source may be in a spectrum aroundan average or within a selected boundary. Accordingly, an X-ray sourceemitting X-rays at a selected energy, such as 120 kilo-electronvolts(keV), may actually be X-rays that are emitted at a range or in aspectrum around this amount. Accordingly, the attenuation may bedifferent for each of the particular X-ray energies.

Further, similar materials may attenuate X-rays in a similar manner,such as soft tissue or hard tissue of a subject. Various non-tissuematerials, such as metal objects (e.g. implants, instruments, etc.) mayattenuate X-rays in a substantially different manner. For example,non-tissue materials may attenuate and/or reflect or scatter X-rays awayfrom the item in the field of view (FOV) of the X-ray source ordetector. It is understood that non-tissue materials may include itemsor materials other than metal, such a polymers, composite materials, orthe like.

An image, such as a 2D projection, may include a plurality of effects(e.g. distortions) due to various non-tissue items within the FOV. Thedistortion may generate artifacts that are accumulated or magnified whengenerating a reconstruction based on a plurality of projections.Accordingly, removal of the distortions and the projections andinclusion of known effects of the selected components or items in thefield of view may be inpainted to the rejections which are then used forthe reconstruction. A reconstruction may include information based uponthe facts of known components within an X-ray system to reduce oreliminate distortion and artifacts and a reconstruction.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is an environmental view of an operating theatre including anoptional imaging system and a navigation system;

FIG. 2 is a schematic illustration of an instrument for inserting animplant into a patient;

FIG. 3 is a schematic illustration of an implant in a subject;

FIG. 4 is a flowchart of a process for reducing artifacts or distortionin an image;

FIG. 5 is an illustration of a projection without and with inpainting;and

FIG. 6 is an illustration of a reconstruction without and withinpainting.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

With reference to FIG. 1 and FIG. 2, a diagram illustrating a procedurearea is shown. The procedure area may include a surgical suite. Placedfor use in the surgical suite may be a navigation system 10 that can beused for various procedures. The navigation system 10 can be used totrack the location of an item, such as an implant or an instrument (asdiscussed herein), relative to a subject, such as a patient 14. Itshould further be noted that the navigation system 10 may be used tonavigate any type of instrument, implant, or delivery system, including:guide wires, arthroscopic systems, orthopedic implants, spinal implants,deep brain stimulation (DBS) leads, cardiac pacing leads, ablationinstruments, etc. Moreover, the instruments may be used to navigate ormap any region of the body. The navigation system 10 and the varioustracked items may be used in any appropriate procedure, such as one thatis generally minimally invasive or an open procedure.

The procedure room may further include an imaging system 12. The imagingsystem 12 may, in various embodiments, interface with the navigationsystem 10. The imaging system 12 may be used to acquire pre-operative,intra-operative, post-operative, or real-time image data of the patient14. In various embodiments, the imaging system 12 may be used to acquireimages at a selected time for confirmation and/or determining progressof a selected portion of a procedure. It will be understood by oneskilled in the art, any appropriate subject can be imaged and anyappropriate procedure may be performed relative to the subject. Thesubject 14 may be a human patient and the procedure may be a surgicalprocedure, such as an implantation of a device (e.g. a screw, lead,etc.).

Exemplarily illustrated in FIG. 1, the imaging system 12 comprises anO-arm® imaging device sold by Medtronic Navigation, Inc. having a placeof business in Louisville, Colo., USA. The imaging device 12 may have agenerally annular gantry housing 20 that encloses an image capturingportion 22. The image capturing portion 22 may include an x-ray sourceor emission portion 26 and an x-ray receiving or image receiving portion28 (also referred to as a detector to detect the x-rays having past thesubject 14) located generally or as practically possible 180 degreesfrom each other within the gantry housing 20. The x-ray emitting portion26 may emit or generate a cone beam 26 x of x-rays. The x-rays in thecone beam 26 x will generally encompass a field-of-view, which mayinclude at least a portion of the subject 14, such as a vertebra 124.The detector 28 may detect the x-rays that have passed through thesubject 14. The x-rays may, however, be attenuated and/or scattered dueto the subject or items in the cone beam 26 x. Further, the detector maydetect and/or generate two-dimensional (2D) image data or projections.

In various embodiments, the x-ray source or emission portion 26 and thex-ray receiving or image receiving portion 28 may be mounted on a rotor(not illustrated) relative to a track (not illustrated) within thegenerally annular gantry housing 20. The image capturing portion 22 canbe operable to rotate 360 degrees during image acquisition. The imagecapturing portion 22 may rotate around a central point or axis, allowingimage data of the patient 14 to be acquired from multiple directions orin multiple planes. The imaging system 12 can include those disclosed inU.S. Pat. Nos. 7,188,998; 7,108,421; 7,106,825; 7,001,045; and6,940,941; all of which are incorporated herein by reference. Theimaging system 12, however, may also include or be replaced with otherimaging systems including C-arm fluoroscopic imaging systems, computertomography (CT) imaging systems, etc. which can also generatethree-dimensional views of the patient 14.

The position of the image capturing portion 22 can be precisely knownrelative to any other portion of the imaging device 12. In addition, asdiscussed herein, the precise knowledge of the position of the imagecapturing portion 22 can be used in conjunction with a tracking system29 to determine the position of the image capturing portion 22 and theimage data relative to the subject, such as the patient 14, which istracked. For example a patient tracking device 48 may be placed on thepatient 14 to track the patient 14.

The tracking system 29 can include various portions that are associatedor included with the navigation system 10. The tracking system 29 canalso include a plurality of types of tracking systems including anoptical tracking system that includes an optical localizer 40 and/or anelectromagnetic (EM) tracking system that can include an EM localizer42. The optical localizer 40 may “view” or optically track trackableportions (tracking devices) with cameras. The EM localizer 42 maygenerate a field and a trackable portion (e.g. EM tracking device) maysense the field to determine a location relative to another trackingdevice in the field. Various tracking devices, including those discussedfurther herein, can be tracked with the tracking system 29 and theinformation can be used by the navigation system 10 to allow for adisplay of a position of an item. Briefly, tracking devices, such as apatient tracking device 48, an imaging device tracking device 50, and aninstrument tracking device 52, allow selected portions of an operatingtheater to be tracked relative to one another with the appropriatetracking system 29, including the optical localizer 40 and/or the EMlocalizer 42.

It will be understood that any of the tracking devices 48, 50, 52 can beoptical or EM tracking devices, or both, depending upon the trackinglocalizer used to track the respective tracking devices. It will befurther understood that any appropriate tracking system can be used withthe navigation system 10. Alterative tracking systems can include radartracking systems, acoustic tracking systems, ultrasound trackingsystems, and the like.

An exemplarily EM tracking system can include the STEALTHSTATION® AXIEM™Navigation System, sold by Medtronic Navigation, Inc. having a place ofbusiness in Louisville, Colo. Exemplary tracking systems are alsodisclosed in U.S. Pat. No. 8,644,907, issued Feb. 4, 23012, titled“Method And Apparatus For Surgical Navigation”; U.S. Pat. No. 7,751,865,titled “Method And Apparatus For Surgical Navigation”, issued Jul. 6,2010; U.S. Pat. No. 5,913,820, titled “Position Location System,” issuedJun. 22, 1999 and U.S. Pat. No. 5,592,939, titled “Method and System forNavigating a Catheter Probe,” issued Jan. 14, 1997, all incorporated byreference herein.

Further, for EM tracking systems it may be necessary to provideshielding or distortion compensation systems to shield or compensate fordistortions in the EM field generated by the EM localizer 42. Exemplaryshielding systems include those in U.S. Pat. No. 7,797,032, titled“Method and system for navigating a catheter probe in the presence offield-influencing objects”, issued on Sep. 14, 2010 and U.S. Pat. No.6,747,539, titled “Patient-shielding and coil system”, issued on Jun. 8,2004, all of which are incorporated herein by reference. Distortioncompensation systems can include those disclosed in U.S. Pat. No.6,636,757, titled “Method and apparatus for electromagnetic navigationof a surgical probe near a metal object”, issued on Oct. 21, 2003, allof which are incorporated herein by reference.

With an EM tracking system, the EM localizer 42 and the various trackingdevices can communicate through an EM controller 44. The EM controllercan include various amplifiers, filters, electrical isolation, and othersystems. The EM controller 44 can also control the coils of thelocalizer 42 to either emit or receive an EM field for tracking. Awireless communications channel, however, such as that disclosed in U.S.Pat. No. 6,474,341, entitled “Surgical Communication Power System,”issued Nov. 5, 2002, herein incorporated by reference, can be used asopposed to being coupled directly to the EM controller 44.

It will be understood that the tracking system may also be or includeany appropriate tracking system, including a STEALTHSTATION® TREON®,and/or S7™ Navigation System having an optical localizer, similar to theoptical localizer 40, sold by Medtronic Navigation, Inc. having a placeof business in Louisville, Colo. Optical tracking systems may alsoinclude those discloses in U.S. Pat. No. 8,010,177, Aug. 30, 2011,Intraoperative Image Registration”; U.S. Pat. No. 6,235,038, issued onMay 22, 2001, titled “System For Translation Of Electromagnetic AndOptical Localization Systems”, all incorporated herein by reference.Further alternative tracking systems are disclosed in U.S. Pat. No.5,983,126, to Wittkampf et al. titled “Catheter Location System andMethod,” issued Nov. 9, 1999, which is hereby incorporated by reference.Other tracking systems include an acoustic, radiation, radar, etc.tracking or navigation systems.

The imaging system 12 can include a support housing or cart 56. Theimaging system 12 can further include a separate image processing unit58 that can be housed in the cart 56. The navigation system 10 caninclude the navigation processing unit 60 that can communicate orinclude a navigation memory 62. The navigation member 62 may include anyappropriate non-transitory memory including a random access memory,magnetic media drive, etc. Further, the navigation memory 62 may beintegrated with the navigation processing unit 60 or remote from thenavigation processing unit 60. The navigation processing unit 60 canreceive information, including image data, from the imaging system 12and tracking information from the tracking systems 29, including therespective tracking devices 48-52 and the localizers 40-42. Image datacan be displayed as an image 64 on a display device 66 of a workstationor other computer system 68.

The workstation 68 can include appropriate input devices, such as akeyboard 70. It will be understood that other appropriate input devicescan be included, such as a mouse, a foot pedal or the like. Further, thevarious processing units, as discussed above, may be incorporated intothe workstation or computer system 68. Thus, the various inputs may beused by the user 54 to include commands to the system. Further, thenavigation member 62 or other appropriate and/or similar memory may beused to transfer or for recall of information, such as image data and/orinstructions for execution by the selected processing units. The variousprocessing units, computers, and/or workstations may include internal orlocal memory and processing units. The processing units may includecentral processing units that are general computers that executeinstructions to perform tasks on a chip. The processing units may alsobe specific circuits, such as application specific integrated circuits(ASIC). Accordingly, the processing units may be devices that receiveinformation and execute instructions that are stored or received basedon the information. Further, the memories may include transient andnon-transient memory systems, such as random-access memory, volatile ornon-volatile memory, etc.

The image processing unit 58 may process image data from the imagingsystem 12 and may transmit the image data, before or after selectedprocessing, to the navigation processing unit 60. It will be furtherunderstood, however, that the imaging system 12 need not perform anyimage processing and it can transmit the image data directly to thenavigation processing unit 60. Accordingly, the navigation system 10 mayinclude or operate with a single or multiple processing centers or unitsthat can access single or multiple memory systems based upon systemdesign. Moreover, the processed image data, as discussed herein, may bedisplayed on the display device 66 or any appropriate display device.Thus, the displayed images need not be displayed with a navigationsystem 10.

The patient 14 can be fixed onto a support 72, such as an operatingtable, but is not required to be fixed to the table 72. The table 72 caninclude a plurality of straps 74. The straps 74 can be secured aroundthe patient 14 to fix the patient 14 relative to the table 72. Variousapparatuses may be used to position the patient 14 in a static positionon the operating table 72. Examples of such patient positioning devicesare set forth in commonly assigned U.S. patent application Ser. No.10/405,068, published as U.S. Pat. App. Pub. No. 2004/0199072, entitled“An Integrated Electromagnetic Navigation And Patient PositioningDevice”, filed Apr. 1, 2003, which is hereby incorporated by reference.Other known apparatuses may include a Mayfield® clamp.

Also, the position (including three-dimensional location andorientation) of the patient 14 relative to the imaging system 12 can bedetermined by the navigation system 10 with the patient tracking device48 and the imaging system tracking device 50. As discussed herein, theposition (including three-dimensional location and orientation) relativeto the patient 14 may be determined, at least in part, with imagesacquired of the patient 14. Accordingly, the position (includingthree-dimensional location and orientation) of the patient 14 relativeto the imaging system 12 can be determined. The imaging system 12, suchas the O-arm® can know its position and be repositioned to the sameposition within about 10 microns. This allows for a substantiallyprecise placement of the imaging system 12 and precise determination ofthe position of the imaging device 12. Precise positioning of theimaging portion 22 is further described in U.S. Pat. Nos. 7,188,998;7,108,421; 7,106,825; 7,001,045; and 6,940,941; all of which areincorporated herein by reference. Generally, it may be selected todetermine the position of the image data relative to the patient 14. Forexample, the position, including the orientation relative to thepatient, of the image data may be used to determine a location of aportion of the patient 14.

Subject or patient space and image space can be registered byidentifying matching points or fiducial points in the patient space andrelated or identical points in the image space. The imaging device 12,such as the O-arm® imaging device sold by Medtronic Navigation, Inc.,can be used to generate image data at a precise and known position. Thiscan allow image data that is automatically or “inherently registered” tothe patient 14 upon acquisition of the image data. Essentially, theposition of the patient 14 is known precisely relative to the imagingsystem 12 due to the accurate positioning of the imaging system 12relative to the patient 14. This allows points in the image data to beknown relative to points of the patient 14 because of the known preciselocation of the imaging system 12.

Alternatively, manual or automatic registration can occur by matchingfiducial points in image data with fiducial points on the patient 14.Registration of image space to patient space allows for the generationof a translation map between the patient space and the image space.According to various embodiments, registration can occur by determiningpoints that are substantially identical in the image space and thepatient space. The identical points can include anatomical fiducialpoints or implanted fiducial points. Exemplary registration techniquesare disclosed in U.S. Pat. No. 9,737,235, issued Aug. 22, 2017,incorporated herein by reference.

In various embodiments, the navigation system 10 may be used to assistin performing a procedure. It is understood, however, that thenavigation system 10 is not required. In various embodiments, aprocedure may proceed without the navigation system. The procedure,however, may also use, alone or in combination with the navigationsystem 10, the imaging system 12, can be used to perform selectedprocedures. Selected procedures can use the image data generated oracquired with the imaging system 12. Further, the imaging system 12 canbe used to acquire image data at different times relative to, such asduring, the procedure. As discussed herein, image data can be acquiredof the patient 14 subsequent to a selected portion of a procedure forvarious purposes, including confirmation of the portion of theprocedure.

With continuing reference to FIG. 1, the imaging system 12 can acquireimage data, such as projections of the subject 14. The projections mayinclude 2D projections that are able to be displayed as 2D images. Theimaging system 12 may also be used to generate or reconstruct threedimensional (3D) images of the patient 14. The patient 14 can be placedrelative to the imaging system 12 to allow the imaging system 12 toobtain image data of the patient 14. To generate 3D image data, theimage data can be acquired from a plurality of views or positionsrelative to the patient 14. The positions may be positions around thepatient 14, such as separated by angles by movement of the detector 28relative to the subject 14. Each position may be defined or referred toas an angle or theta (θ) position relative to the patient 14. The 3Dimage or image data of the patient 14 can be used alone or with otherinformation to assist in performing a procedure on the patient 14 or anappropriate subject. It will be understood, however, that anyappropriate imaging system can be used, including magnetic resonanceimaging, computed tomography, fluoroscopy, etc. to acquire image data(including 3D image data) of the patient 14.

As discussed above, the imaging system 12 may include any appropriateimaging system, such as the O-arm® Imaging System sold by MedtronicNavigation, Inc. The O-arm® Imaging System can acquire images of thesubject 14 by acquiring image data of the subject 14 that may includetwo-dimensional projections. The projections are acquired by emittingX-rays from the source 26 and detected at the detector 28. Theprojections may be displayed as two-dimensional images on the displaydevice 66 and/or may be reconstructed into a three-dimensional image,such as the image 64, for display on the display device 66. The image,for example the reconstructed image 64, may include artifacts ordistortion if various items are positioned within the field of view ofthe imaging system, such as within the cone of X-rays 26 x emitted fromthe X-ray source 26 and detected at the detector 28. This distortionrefers not only to the spatial distortion in the reconstructed image,but also includes distortion of the signal recorded by thedetector—e.g., polyenergetic effects (beam hardening) associated withenergy-dependent detector response, and “zero” data or electronic noisecontribution (photon starvation effects). Distortions may be generatedwhen various non-tissue elements or materials, such as a pedicle screw120 that may be driven or moved with an instrument, such as a surgicalmotor 126, are within the X-ray cone 26 x when the subject 14 imaged.For example, according to various embodiments, the pedicle screw 120 maybe implanted into a vertebra 124 in the patient 14. It is understoodthat discussion herein to a single or plural vertebrae is merelyexemplary and generally a procedure maybe performed on any selectednumber of appropriate vertebrae. The pedicle screw 120 may be positionedin the vertebra 124 during a surgical procedure, as is generallyunderstood in the art. The imaging system 12 may then be used to acquireimages after placing the pedicle screw 120 in the subject 14, but priorto completing a procedure, such as placing a connection rod, or otherselected portion of a procedure. Imaging the subject 14 while thepedicle screw 120 is in place, distortion may occur in the imageprojection that causes further distortion and/or artifacts in the imagereconstruction 64 for display on the display device 66. According tovarious embodiments, therefore, a process may be performed, such as byinstructions executed by the navigation processing unit 60 and/or theimaging processing unit 58 or other appropriate processor, to assist inremoving the artifacts and/or accounting for the artifacts fordisplaying a non-distorted image.

The process of removing or accounting for the distortion in the imagesmay be initiated by accounting for or determining artifacts ordistortion in a projection due to a selected item, such as an objectincluding an implant or instrument. The selected item may then bereplaced in projections prior to a reconstruction, where the replacementcan be performed according to a variety of inpainting methods. Theprocess may be developed into an algorithm and instructions basedthereon that are stored in a memory, such as the navigation memory 62 orother appropriate memory, and executed by one or more processors orprocessing units, including those discussed above. A reconstruction withthe correction or artifact reduction may then be displayed on thedisplay device 66 as the image 64.

As discussed above, images may be generated and viewed on the displaydevice 66. The acquired images are acquired with the imaging system 12,which may include the O-arm® Imaging System, at a selected time. Forexample, the images may be acquired during a selected procedure, such asan operative procedure on the subject 14. In various embodiments, theoperative procedure may include positioning an implant into the patient14. The implant may include the pedicle screw 120, or more than onepedicle screw 120, positioned in one or more vertebrae 124. Asillustrated, exemplary, in FIG. 3, first and second pedicle screws 120 aand 120 b are schematically illustrated positioned in the vertebra 124relative to a midline 140. The midline 140 may be displayed on thedisplay device 66 relative to an image, such as the image 64, or may beexemplary of a midline extending from a posterior to an anterior portionof the patient 14. After positioning the pedicle screw 120 in thepatient 14, such as in the vertebra 124, the imaging system 12 may beused to acquire image data of the patient 14, including the vertebra 124having the pedicle screws 120 a and 120 b positioned therein. Asillustrated in FIG. 3, the pedicle screw 120 may be positioned in thevertebra 124 in any appropriate manner, such as with the drill motor ortool 126 by the user 54.

Acquiring image data of the subject 14 after positioning the pediclescrew 120 in the patient may be performed for any appropriate purpose,such as confirmation of positioning the pedicle screw 120 in a selectedor predetermined position. During image data acquisition, particularlyafter the pedicle screws 120 a, 120 b are placed, distortion orartifacts in the image 64 may hinder or slow confirmation of the corrector accurate position of the pedicle screw 120 in the vertebrae 124.Accordingly, as discussed further herein, a selected process may be usedto reduce and/or correct for distortion or errors in the acquired imagedata before or prior to generating the image 64, which may include areconstruction such as a three-dimensional reconstruction, based uponone or more projections acquired of the subject 14 with the imagingsystem 12.

Turning reference to FIG. 4, a process or flowchart 200 illustrates anefficient process for removing or accounting for artifacts inprojections and later reconstructions, such as the image 64, of thesubject 14 for viewing by the user 54. The process 200 allows for anefficient, including lower computational time and/or necessaryresources, to generate the image 64 for viewing by the user 54 withoutartifacts and/or showing a clear or high contrast edge of a selecteditem. In various embodiments, the selected item may include the pediclescrew 120 positioned in the vertebra 124. In various embodiments,computational time may be lowered to less than about three minutes,including less than about two minutes for generating a reconstructionwith inpainted objects, as discussed herein, with the process 200. Theremoval of the artifacts may allow for a more precise and clear imageand/or distinction between the selected item, such as the pedicle screw120 and in surrounding areas, such as the vertebra 124. It will beunderstood that the positioning of the pedicle screw 120 in thevertebrae 124 is exemplary and contrast and/or distortions may occurbetween any differing materials. Accordingly, discussion of the pediclescrew 120 relative to the vertebrae 124, herein, is exemplary unlessspecifically identified otherwise.

Also, it is understood that the pedicle screw 120 may be formed of oneor more selected material (e.g. metal or metal alloy) that affectsX-rays when generating X-ray image data in a manner to cause distortionor artifacts relative to the X-rays that generate the image data of thevertebrae 124. Therefore the process 200 may be used to remove oraccount for the artifacts in the image data when generating the image 64for display with the display device 66. It is further understood thatthe pedicle screw 120, or other selected item, may be formed of orinclude a plurality of materials.

With continued reference to FIG. 4 the process 200 is understood to bean image analysis and/or reconstruction process 200 that may beperformed alone and/or in part of a selected procedure, such as asurgical procedure including positioning the pedicle screw 120 in thevertebrae 124. The process 200, therefore, may also be an algorithm, orinclude algorithmic portions, that may be executed by a selectedprocessor or processor system, such as the imaging processing unit 58discussed above. It is understood, however, that any appropriateprocessing system may be used to execute the process 200 to generate animage for display on the display device 66.

The process 200 may be incorporated into other procedures, such as asurgical procedure including placing a selected item, such as thepedicle screw 120. The selected procedures, therefore, may includestarting a procedure in block 204 and then preparing a subject forprocedure in block 206. Preparing the subject for procedure in block 126may include predetermining or selecting a location for the pedicle screw120, or other appropriate implant, within the subject 14. Suchpreplanning or predetermination may include acquiring preoperative imagedata of the subject 14 and planning a position for the pedicle screw 120in the vertebra 124. Further, preparing the subject may include movingthe subject 14 into the operating theatre on the support 72, forming anincision of the subject 14, positioning instruments relative to thesubject 14, or other appropriate procedure steps.

After preparing a subject for a procedure in block 206, placing aselected item in the subject in block 208 may be performed. As discussedabove, exemplary embodiments may include positioning the pedicle screw120 in the vertebra 124, as illustrated in FIG. 2. The pedicle screw 120may be any appropriate pedicle screw such as a CD Horizon® Solara® orLegacy® spinal or pedicle screws, sold by Medtronic, Inc. having a placeof business in Minnesota, USA.

With additional reference to FIG. 5, the pedicle screw 120 may includeselected portions, such as a first shank portion 120′ that is positionedwithin the vertebrae and/or a second portion 120″, such as a head orgimbal head portion that is movable relative to the shank. It isunderstood, however, that the pedicle screw 120 may be any appropriatetype of pedicle screw positioned in the patient. It is furtherunderstood that the selected item positioned in block 208 need not be apedicle screw, but may be any appropriate type of item positionedrelative to the subject 14, or any other appropriate portion. Generallythe selected item, such as the pedicle screw 120, is formed of adifferent material (e.g. metal) than the portion in which it is placed,such as the vertebrae 124 (e.g. bone tissue).

After positioning the selected item in block 208, the process 200 may beused to assist in generating a selected or appropriate reconstructionfor viewing by the user 54. The process 200 may include or start withthe acquisition of projections including the selected items in block220. The acquisition of projections in block 220 may include theacquisition of two-dimensional projections of the subject 14. Theacquisition may be a real time image data acquisition, recalling ofimage data, or a combination of both. With continuing reference to FIG.5, projections that are acquired may include those shown in parts (a),(b), and (c). The projections may include the vertebra 124 and thepedicle screw 120.

As illustrated in FIG. 5, the pedicle screw 120 is schematically orexemplary illustrated. The pedicle screw 120 may include variousfeatures such as the shank 120′ the head 120″ and other portions. Theshank 120′ may include a thread or other feature to allow for purchaseor connection with the vertebra 124. The head 120″ may includeadditional features, such as a U-shape and be moveable relative to theshank 120′. The head 120″ may then be fixed to the shank 120′ in aselected manner, such as with a set screw or a nut. It is understoodthat the shank 120′ and the head 120″ may be formed of the same materialor a different material, such as two different metal alloys or one metaland one polymer.

Nevertheless, the pedicle screw 120 may be positioned in the vertebra124 and images may be acquired of the vertebrae 124 and the screw 120positioned therein. For example, as illustrated in FIG. 5, part (b) oneor more of the pedicle screws 120 may be positioned may be positioned inthe patient, such as the vertebra 124. As illustrated in FIG. 5 theimage of the vertebra 124 p is shown and the image of the pedicle screw120 p is shown. The projection may include a two-dimensional projectiongenerated with the imaging system 12 in the field of view. It isunderstood, however, a plurality of projections, for example includingabout 360 projections, may be generated of the subject 14 in the fieldof view including the vertebrae 124 and the pedicle screw 120. Anyappropriate selected number of projections, however, may be acquired andincluded in the process 200. For example, the projection in (b) isdenoted as theta (θ)=180 degrees (°), and, therefore, may be aprojection acquired at 180° from an origin or start point.

As discussed further herein, the projections, as illustrated in FIG. 5,may include a plurality of projections that are acquired in anyappropriate manner. For example, as discussed above, the process 200 maybe executed with the image processing unit 58. Accordingly, the imagingsystem 12 may generate or collect the image data including theprojections and they may be immediately processed with the imagingprocessing unit 58. Alternatively thereto, or in addition thereto, theimage data may be acquired with the imaging system 12 and then may beforwarded or transferred to selected processing units or processors. Forexample, the image data may be transferred with a coupling, such as awired or wireless protocol, saved to a selected memory medium (e.g.CD-ROM, volatile or nonvolatile memory, etc.). Accordingly, it isunderstood by one skilled in the art, that the acquiring projections inblock 220 may include operating the imaging system 12 to acquire imagedata, receiving image data from a selected memory, or transferring theimage data from a selected memory or source to a sourcing unit.

Regardless of the particular method of acquiring the projections inblock 220 that may be further processed, as discussed herein. Each ofthe projections from block 220 may be distorted, in the sense that thesignal levels recorded by the detector 28 are inaccurate. The distortionleads to artifacts in the 3D images reconstructed from thoseprojections, such as streaking or shadows, due to the material of thepedicle screw 120 in the field of view, including the cone 26 x ofX-rays. In FIG. 5 the part (c) illustrates a close up or detail view ofan area of interest (AOI) or field of interest.

The acquisition of the projections in block 220 may include a firstinput for the process 200. Additional inputs may include known componentparameters or known components (KC) in block 226. The known componentparameters may be predetermined parameters of the selected item, such asthe pedicle screw 120. In various embodiments, for example, the KC mayinclude the pedicle screw 120 having the shank 120′ and the head 120″.The known component parameters may further include the type of materialof the selected portions of the pedicle screw 120, such as the shank120′ formed of a stainless steel alloy and the head 120″ being formed ofthe same stainless steel alloy. It is understood, however, that thepedicle screw, such as the shank 120′, may be formed of other materialssuch as titanium or titanium alloys, polymers, or the like.Nevertheless, the known parameters in block 226 may include thespecifics of the selected item, such as the pedicle screw 120.

The known parameters in block 226 may also include selected dimensionssuch as length, width, height, and the like. The known parameters inblock 226 may further include the number of components or portions ofthe pedicle screw 120 and the relative geometry of the variouscomponents or portions of the pedicle screw. For example, the knownparameters in block 226 may include a fixed geometry of the pediclescrew 120 and/or various possible geometries of the pedicle screw 120.As illustrated in FIG. 5, the pedicle screw 120 includes the shank 120′and the head 120″ movable relative to one another. Accordingly, theknown parameters in block 226 may include a range of motion and/ordegree of freedom of motion (e.g. possible geometries) of the shank 120′relative to the head 120″.

The known parameters in block 226 may further include known interactionsof X-rays relative to the selected item, including the pedicle screw120. The known parameters in block 226 may include the knowninteractions of X-rays with the stainless steel forming the shank 120′and the stainless steel forming the head 120″. The known parameters inblock 226 may further include interactions of X-rays with titanium ortitanium alloys, polymers, or other materials that may form the pediclescrew 120. The known interactions of the KC may include the amount ofattenuation, the amount of scattering, the amount of absorption, orother selected parameters of X-rays relative to materials of the pediclescrew 120. The known component parameters may be determined via testingprior to the process 200 and saved for further access. Further, the KCmay relate to a specific item, such as the pedicle screw 120, that isinput or used to select a specific, including singular, KC in block 226.

The known component parameters, also referred to as parameters of thecomponent or object (e.g. the pedicle screw 120), may be defined invarious manners, such as those discussed above, including exact valuesand/or defined or determined during a selected process. Exact values orparameters may be based upon specifications of the object (e.g.predetermined and/or known technical specifications of the object). Thespecifications of the object may include the features, such as thoseidentified above, including a length, diameter, interaction with apolyenergetic x-ray beam, or other features. These values may be exactor nearly exact, such as knowing the exact width or range length,diameter, or the like, such as within selected tolerances. In variousembodiments, however, the parameters may also be determined or definedduring a selected process. As discussed herein, the object may bedetermined or registered in the projections based upon a selectedprocess, as discussed further herein. During the registration processthe object may be parametrically defined and/or determined in theacquired projections. By defining the parameters during a registrationprocess, a determination may be made during the selected procedure ofthe parameters including a length, diameter, or the like. These may bebased upon analysis of the image or require projections based uponselected known or assumed interactions with an x-ray beam, or otherfeatures. Accordingly, the parameters may be predetermined, as discussedabove and noted herein, and/or determined during a registration processby analyzing the image data acquired in the projections.

In various embodiments, therefore, the known component parameters inblock 226 may be representations, such as a lookup table, of theselected item including the pedicle screw 120. Further, the knownparameters in block 226 may include selected specific models, such as acomputer aided design (CAD) model of the pedicle screw 120 includingknown materials thereof and known interactions of X-rays relativethereto. In various embodiments, the pedicle screw 120 is the CDHorizon® Solara® implantable pedicle screw and the known componentparameters in block 226 may include a CAD model of the specific pediclescrew (including a specific model number and/or geometry and dimensionsthereof) or a deformable spline model (such as a spline model of acylindrical wire, needle, or rod) along with known materials, knowninteraction of materials, and the like. The known parameters in block226 may then be accessed, such as recalled with the processing unit 58,for further portions of the process 200.

With continued reference to FIG. 4, once the projections are acquired inblock 220 and the known parameters are acquired or accessed in block226, a registration, also referred to as a known component (KC)registration may occur in a sub-block or sub-process 240. The KCregistration in block 240 may include various steps or processesincluding a forward projection in block 250. The forward projection inblock 250, as discussed further herein, may then be compared to theprojections in block 260. Based upon the comparison in block 260 asimilarity metric (GC) may be determined in block 270. The comparison inblock 260, yielding the similarity metric in block 270, may then beoptimized in block 280. In particular, the optimizer block 280 maygenerate a transformation that is again applied to a forward projectionin block 250 to determine a similarity metric in block 270 based upon acomparison in block 260. Accordingly, the KC registration in block 240is an iterative process until the optimizer in block 280 determines anoptimized transformation.

An optimized transformation may be a convergence where the differencesbetween the forward projection in block 250 and the projections in block260 are substantially small or have a selected similarity metric inblock 270. At the selected transformation of similarity metric, thetransformation is determined to have converged or been optimized as anoptimized transform ({circumflex over (T)}) and may be used for areconstruction process 290. The reconstruction process 290 is understoodto be a sub-process of the artifact or noise reduction process 200. Thereconstruction process 290 will be discussed further herein and,briefly, generally combines the acquired projections from block 220 withthe optimized or converged transform from block 280.

Returning to the KC registration process 240, the KC registrationprocess 240 includes a registration of the known components from block226 with a selected number of projections, including less than or all ofthe acquired projections from block 220, that may be used for a laterreconstruction in the reconstruction sub-process 290. In particular, theKC registration attempts to determine the portion in the acquiredprojections from block 220 that match to the known component in block226. For example, one or more pixels in one or more of the projectionsare generated by the selected item (e.g. pedicle screw 120) positionedwithin the subject in block 208 and therefore should match a forwardprojection of the known component from block 226. For example, asdiscussed above, the pedicle screw 120 may have precise parameters knownthat define the known component parameters in block 226. Accordingly,the known parameters may be input as represented by K. A digitalradiograph reconstruction or digitally reconstructed radiograph (DRR)forms the forward projection in block 250 and may be defined by Equation1 (Eq. 1):

{circumflex over (p)}(κ,T)=∫_({right arrow over (r)})κ(T)d{right arrowover (r)} ²  Eq. 1

In Eq. 1, the forward projection {circumflex over (p)} is a projectionof the known component. In particular, Eq. 1 includes a DRR formed fromthe input known parameters κ from block 226, which may include a meshmodel of the selected item that is a line integral along a ray {rightarrow over (r)} incident on the transformed KC κ. Accordingly, theforward projection {circumflex over (p)} is a digitally reconstructedradiograph (also referred to as a mask herein) based upon the knowncomponent parameters κ from block 226 that may be compared to theacquired projection (also referred to herein as p). One or more selectedtransformation models (T) may be employed, such as a rigid homogeneoustransform or a deformable b-spline function. Generally, only onetransformation model may be selected in any specific application, butvarious appropriate models may be selected or the transformation (T).Furthermore, select parameters of κ may be included within theoptimization process, for example to model the unknown diameter of atool with a cylindrical profile.

The forward projection as defined in block 250 may be compared in block260 to the acquired projections p from block 220. The comparison inblock 260 may allow for the output of the similarity metric which, invarious embodiments, is defined as a gradient correlation (GC). WhileGC, according to Equation 2 (Eq. 2), is an appropriate similaritymetric, it is understood that other similarity metrics may also be used.Regarding GC, however, Eq. 2 includes:

$\begin{matrix}{{G{C\left( {p,\overset{\hat{}}{p}} \right)}} = {\frac{1}{2}\left\{ {{NC{C\left( {{\nabla_{x}p},{\nabla_{x}\overset{\hat{}}{p}}} \right)}} + {NC{C\left( {{\nabla_{y}p},{\nabla_{y}\overset{\hat{}}{p}}} \right)}}} \right\}}} & {{Eq}.\mspace{11mu} 2} \\{{and}\mspace{14mu}{Equation}\mspace{14mu} 3\mspace{14mu}\left( {{Eq}.\mspace{14mu} 3} \right)\text{:}} & \; \\{{N\; C\;{C\left( {a,b} \right)}} = \frac{{\Sigma_{i}\left( {a_{i} - \overset{\_}{a}} \right)}\left( {b_{i} - \overset{\_}{b}} \right)}{\sqrt{{\Sigma_{i}\left( {a_{i} - \overset{\_}{a}} \right)}^{2}}\sqrt{{\Sigma_{i}\left( {b_{i} - \overset{\_}{b}} \right)}^{2}}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

The GC generally looks for gradients (also referred to as high contrastregions or edges) between the forward projection {circumflex over (p)}in block 250 and the acquired projections in block 220. According to Eq.2 and Eq. 3, the GC is defined as a sum of normalized cross-correlation(NCC) of orthogonal image gradients. For example, the NCC defines thecorrelation of the normalized intensities of image gradients a and b forimages p and p, respectively. Therefore, the GC, as illustrated in Eq.2, is a sum of the gradients between the forward projection from block250 and the acquired projections from block 220.

The optimizer in block 280 is then used to determine whether theconverged transform {circumflex over (T)} has been found or achieved. Inparticular, the convergence is defined by Equation 4 (Eq. 4):

$\begin{matrix}{\overset{\hat{}}{T} = {\arg{\max\limits_{T}{\sum_{\theta}{G{C\left( {p_{\theta},{{\overset{\hat{}}{p}}_{\theta}\left( {\kappa,\ T} \right)}} \right)}}}}}} & {{Eq}.\mspace{14mu} 4}\end{matrix}$

which may be iteratively solved between the forward projection in block250 and the acquired projections from block 220. Eq. 4 is used todetermine the greatest similarity between the forward projection inblock 250 and the acquired projections in block 220. The iterationoccurs by determining the GC in block 270 based upon the comparison inblock 260 and then transforming the forward projection from theoptimizer in block 280 to a different forward projection in block 250.Accordingly, the optimizer block may determine whether the similarlymetric in block 270 is the same or has been optimized and/or within aselected threshold of change, for example when the mean change in T issmaller than about 0.01 millimeters (mm) to about 0.2 mm, includingabout 0.1 mm and about 0.01 degrees to about 0.2 degrees, includingabout 0.1 degrees. The threshold may also or alternatively include orwhen changes in in the similarity metric GC approach the machineprecision (such as an image processing unit 58) for representingfloating-point numbers.

If the optimizer in block 280 determines that a threshold has not beenreached then a NO path 282 may be followed to the forward projectionblock 250. The forward projection may then be altered, such asdetermining a forward projection at a different perspective relative tothe known component in block 226 to form a new forward projection forcomparison to the acquired projections from block 220. If the optimizerblock 280 determines at a convergence has been achieved (e.g. adifference from a present GC is within a threshold relative to a priorGC) then the converged or optimized transform may be output with the YESpath 284.

Appropriate optimization techniques may be used in the optimizer block280, such as those that may be executed by the processing unit 58, orother appropriate processing unit. In various embodiments, a covariancematrix adaptation evolution strategy may be used to achieve theoptimization. The selected strategy may include a stochastic derivativefree optimization method. It is understood, however, that otherappropriate optimization methods or techniques may be used in theoptimizer block 280.

Once the Yes path 284 is followed to output the optimizedtransformation, the optimized transformation ({circumflex over (T)}) maybe used for modifying the projections acquired in block 220.Modification to the projections acquired in block 220 may be madeaccording to any appropriate process, including those discussed furtherherein. In various embodiments, inpainting in a selected manner may beperformed in a modification block 310, as discussed further herein.Inpainting may include generally known digital inpainting such as aninterpolation based inpainting of the acquired projections. Duringinterpolation based inpainting, the pixels or voxels identified as apart of the component or object (e.g. the pedicle screw 120) may bereplaced with pixels or voxels of a selected type or manner. Forexample, the identified pixels, based upon the above described process200, may be replaced with a selected model or graphical representationof the object (e.g. the pedicle screw 120). In addition oralternatively, the identified pixels or voxels may be replaced with aselected color or feature in the acquired projections that have beenidentified as the object. In addition to the direct inpainting from aselected model, interpolation may be made determined or identified orreplace pixels that are at edges or between identified object pixels orvoxels or non-identified pixels or voxels. Moreover, a selected amountof noise, such as an optional random noise component, may be added tothe inpainted voxels or pixels to selectively characterize therepresentation of the object in the projections.

In addition to a direct and/or interpolation based inpainting, variousother processes may be used to assist in or preform inpainting. Forexample, a machine learning process or system may be used to perform theinpainting into the projections. For example, the pixels or voxelsidentified in the process 200 may be inpainted based upon prior trainingof a machine learning system. For example, a neural network (e.g. a deeplearning system) may be used to determine pixels or voxels to beinpainted based upon training of previously determined objectprojections and the identification of the object on the projection andthe inpainting therein. In various embodiments, therefore, inpaintingmay replace voxels or pixels in a projection according to an appropriatesystem such as an interpolation or machine learning base system.

The modification of the projections in block 310 may also includedetermining or estimated pixel values, such as calculating or computingpixel or voxel values using a selected modeling of an imaging system,such as of the x-ray beam. As discussed above the x-ray beam may includex-rays that are emitted by the emitter 26. The x-rays in an emitted beammay be polyenergetic, such as including a spectrum. Accordingly, thex-rays emitted may not be of only a single frequency or power. Thepolyenergetic x-ray beam may interact with material in a known mannerbased upon the polyenergetic identity of the x-ray beam. Theinteractions may be known based upon the known components, as discussedabove, of the various x-ray components (defined by the x-ray spectrum)with the object in the projections. Accordingly, the determined pixelvalues based upon the known polyenergetic model of the x-ray beam may beused to generate pixel or voxel values in the projections and thereforemay be used to replace the determined pixels in the projections.

As discussed above, the projections may be modified in various mannersand in appropriate processes. Discussion herein to inpainting is merelyexemplary, and not intended to limit the scope of the subject disclosureof the following claims. Accordingly, modifying may include inpaintingin the projections acquired in block 220 at modifying (e.g. inpainting)block 310. The inpainting block 310 is the first process or step of thereconstruction process 290. The reconstruction process 290 may also bereferred to as a metal artifact reduction or removal (MAR) process.Accordingly, the MAR reconstruction may be used to reduce or removeartifacts due to the selected item, such as the pedicle screw 120. Byreducing the metal artifacts, or other selected artifacts, in theinpainting block 310, the artifacts are removed for the laterreconstruction. Reconstruction may include or be based on a backprojection reconstruction including a filtered back projection (FBP). Invarious embodiments, the back projection may be a three-dimensional (3D)projection in block 320. A reconstruction occurs in block 330 which mayform the reconstruction of the image 64 for viewing on the displaydevice 66.

With continuing reference to FIG. 4 and FIG. 5, inpainting block 310uses the optimized transformation to inpaint the acquired projectionsfrom block 220. As illustrated in process 200, the projections (p) areinput with the optimized transformation or converged transformation{circumflex over (T)} into inpainting block 310. In the inpainting block310, the surrounding pixels of projections (p) may be used tointerpolate the region identified by the forward projection of the KC.Alternatively, the DRR of the forward projection ({circumflex over (p)})that accounts for the various effects of x-ray and metal interaction maybe painted into the acquired projection 220 at the registered positionbased on the optimized transform {circumflex over (T)} from theoptimizer block 280. In other words, selected polyenergetic signalmodels informed by the KC model of the component shape and materialcontent, based on known material interactions with X-rays included inthe forward projection, may be used to paint into the acquiredprojection 220 at the registered position. Accordingly, the pixels inthe acquired projections 220 that match or have the greatest similaritymetric to the forward projection from block 250 are replaced with theforward projection from block 250 in the inpainting block 310.

As noted above, with reference to FIG. 5, the projection from block 220,or one of the projections, includes the vertebrae 124 p and the imagedscrew 120 p. Once the transformation is optimized in block 280 theforward projection that is optimized or best matches the screw 120 p inFIG. 5 part (b) may be replaced or inpainted with the forward projectionfrom block 250. As illustrated in FIG. 5 part (e), an inpainted screw120 ip (schematically illustrated by a dotted line in part (f)) may beinpainted or used to replace the screw 120 p in the projection andreplace it in the image, including the vertebrae 124 p. As discussedabove the acquired projections in block 220 may include one or more ofthe projections acquired of the subject 14. In various embodiments thenumber of projections may include three projections, six projections,all of the projections, or any appropriate number. In variousembodiments, the acquired projections in block 220 may include sixprojections that are offset or displaced from one another by 30 degrees(or any appropriate selected angle theta (θ) around the subject 14. Thesimilarity metric in block 270 and the optimized transformation in block280 may be for only a portion or selected number of the projections ofthe subject 14. However, it is understood, that the use of the knowncomponent parameters in block 226 may minimize or allow for a fast andefficient registration based upon a forward projection in block 250 thatsimilarly or most closely matches the actual projections in block 220due to the known component parameters in block 226. THE KC parameters,again, may include size, shape, material, and interaction with X-rays.Nevertheless the inpainting in block 310 may replace the identifiedscrew 120 p with the inpainted forward projection that has beenregistered thereto as discussed above. The projection may then become aninpainted projection, such that the inpainted projection in FIG. 5 part(e), in block 310 including the inpainted selected portion or item.

The inpainting in block 310 may also include various optimization orrobustness features. For example, the forward projection from block 250,which may also be referred to as a mask, may be dilated or expandedrelative to the exact, known component parameters from block 226relative to the projections from block 220. In various embodiments, theforward projection mask from block 250 may have a dilation or be dilatedone or more pixels when inpainting on the projection in block 310. Thedilation may assist in overcoming errors such as manufacturingvariation, geometric calibration of the imaging system, floatingprecision errors, or other possible errors. The selected amount ofdilation or expansion of the mask assists in ensuring appropriatepositioning or accounting for errors, as noted above. The finalreconstruction, as discussed herein, which may be the image 64 wouldinclude the dimensions of the KC parameters from block 220 to illustratethe extent or placed (implanted) final position of the pedicle screw 120in the vertebrae 124.

Further, the optimized transformation from block 280 identifies theselected item in the projection to be inpainted in block 310. Theinpainting process or method may be selected from appropriate methods.For example, inpainting may include a linear interpolation in theselected projection. In various embodiments, the linear interpolation isachieved by producing a Delaunay triangulation over a convex hull of theregions (e.g. Quickhull algorithm disclosed in Barber, C. B., Dobkin, D.P., and Huhdanpaa, H. T., “The Quickhull algorithm for convex hulls,”ACM Trans. on Mathematical Software, 22(4):469-483, 1996) masked (suchas with the DRR of the forward projection 260) by the identifiedtransformation from block 280 followed by a barycentric interpolation oneach produced triangle. The inpainting process (including in variousembodiments, at least one of the interpolation-based or the model-basedthat exercises the KC model) is then repeated for all of the projections(such as all of the projections acquired in block 220) and measurementsin each of the projections input in block 220.

Once the modification in block 310, such as including inpainting in theprojections from block 220, is completed, a reconstruction may beperformed in block 320 with the modified projections. The reconstructionmay be any appropriate reconstruction, as discussed herein. Thereconstruction may be used for various purposes as discussed herein.

In various embodiments, the reconstruction in block 320 may include athree-dimensional filtered back projection (3D FBP). In exemplaryembodiments, the 3D FBP may include the Feldkamp-Davis-Kress algorithmreconstruction method generally known in the art. It is understood,however, that other appropriate reconstruction (e.g. alternative backprojection) methods may be used.

In addition to and/or alternative to the filtered back projection, aniterative reconstruction may also be performed. The iterativereconstruction may include a model based iterative reconstruction (MBIR)algorithm. The iterative reconstruction may include iteratively alteringparameters of a model to achieve or minimize a difference between themodel and the modified projections from block 310. For example, a modelof the object, such as the pedicle screw 120, may be identified and aprojection through the model may be iteratively altered to match themodified projections from block 310. When a match is achieved, the modelmay be used to assist in the reconstruction of the model projections.

Based upon the back projections from block 320, the reconstructionprocess 290 may output the reconstructed image in block 330. Thereconstructed image may be a visualization of the reconstruction. Thevisualization may be displayed as an image for viewing, such asdisplayed as an image with the display device 66.

The outputted reconstruction in block 330 may be referred to as a KC-MARreconstruction and/or a visualization (e.g. a KC-MAR reconstructionvisualization). The output, including the visualization, may include orbe represented as the image 64 for display on the display device 66 forviewing by the user 54. The reconstruction may include athree-dimensional reconstruction and/or may illustrate the backprojections as images for viewing by the user. With reference to FIG. 6a back projection of uncorrected acquired projections in block 220 isillustrated in row A. A reconstruction using the process 200, includingthe KC registration 240 and the reconstruction process 290, isillustrated in row B. As clearly illustrated in FIG. 6, row B, havingthe inpainted registered known components, reduces metal artifacts orselected distortion. The distortion reduction allows for viewing orreconstruction visualization that includes sharper or higher contrastedges with reduced or minimal streaking and other artifacts in thereconstruction.

As illustrated in FIG. 6 row B, the reconstruction visualization mayalso include selected information based upon the know components fromblock 226. As discussed above, the inpainting in block 310 may beinpainted with the mask from the forward projection in block 250. Theforward projection in block 250 includes the known components parametersfrom block 226. Accordingly, the inpainting may include variousgeometric configurations, such as size, shape, and configuration, andthe mask of the forward projection from block 250 may also includedifferentiation of materials due to different attenuation due todifferent materials of the known components. For example, as discussedabove, the head 120″ of the pedicle screw 120 may be a differentmaterial or formed of a different material than the shank 120′.Accordingly, the reconstruction in FIG. 6 row B may differentiate, suchas due to grayscale, the reconstructed portions of different materials.In various embodiments, therefore, the reconstructed projection of thehead 120″r may have a different or altered greyscale or visual effectfrom the shank 120′r. This is due, at least in part, to the forwardprojection from block 250 being based upon the known componentparameter. The KC parameters in block 226 may be exhaustive regardingthe known component, such as the pedicle screw 120.

As the known component parameters may include size and geometry and alsoinclude materials, the effects of each may be known and applied forforming the forward projection and the inpainting in block 310. Again,as discussed above, the known components and their effects on the X-rayprojections may be predetermined and known and saved and recalled forthe forward projection in block 250 and the inpainting in block 310. Theback projection reconstruction in block 320 and a reconstructionvisualization or output in block 330, respectively, may therefore alsobe based upon the known component parameters from block 226.

The reconstruction visualization, or the visualization in block 330, maybe generated in various formats and/or selected by a user from one ormore options. The visualization may include a direct reconstruction ofthe modified projection from block 310. For example, the reconstructionfrom block 320 may be displayed for viewing by the user 54. Thereconstruction, as discussed above, may include incorporating themodified projections directly into a reconstruction projection. Theplurality of projections or a selected plurality of projections may beused to generate a three-dimensional (3D) model or visualization forviewing by the user 54. Accordingly, the visualization in block 330 maybe a direct visualization or visualization of the direct reconstructionfrom block 320.

In various embodiments, the visualization may also include and/oralternatively include picture or image elements (e.g. voxels or pixels)that coincide with a registered object in the modified projections fromblock 310. For example, once the object is registered, as discussedabove, the projection may have the pixels or voxels that coincide or areregistered as the object is replaced with a selected other pixels orvoxels. For example, selected color, gradient, or type of pixel or voxelmay be used to replace the registered voxel in the visualization inblock 330. Accordingly, an additional or alternative visualization maynot be required or generated, just that the pixel or voxels related tothe registered object may be replaced.

As a further alternative and/or additional visualization, selectedslices or 2D portions may be displayed relative to a selected feature orparameter of the object. For example, once the object has beenidentified or registered in the projections (e.g. the pedicle screw 120)slices that include the object and/or coincide with the object may beoriented or re-oriented and illustrated in a selected manner, such asalong a long axis of the object. For example, as illustrated in FIG. 6,the illustration or visualization for display may be oriented such thata long axis 102L of the screw 120 is used to orient the visualization.Therefore, the long axis 102L may be used to orient the imagesvertically and if a plurality of slices or 2D images are displayed theymay all be displayed substantially in parallel.

As a further alternative and/or addition, a graphical representation maybe superimposed or overlaid on the selected image. For example, asdiscussed above, the object may include the pedicle screw 120. Further,the object may be determined and/or identified based upon knowncomponents, which may include a model of the object. Accordingly, aselected portion or version of the object (such as a representation oroutline thereof) may be displayed relative to the image. In variousembodiments, for example, the graphical representation may be overlaidor superimposed on the image at the registered location of the object.

Accordingly, the visualization in block 330 may include any appropriatevisualization. The visualization may be based upon the registered orknown position of the object, such as the pedicle screw 120, in theacquired projections. The visualization may then be displayed on thedisplay device 66, such as the image 54, for viewing by the user 54 forvarious purposes. In various embodiments, therefore, the littleartifacts may be reduced in the visualization block 330 such that theuser 54 may view the visualization 64 on the display device 66 withsubstantially reduced and/or eliminated distortions or artifacts due tometaled or other component in the image.

In light of the above, the final reconstruction and/or reconstructionvisualization in block 330, which may be displayed as the image 64 onthe display device 66, may have substantially reduced or eliminatedartifacts due to altered attenuation or distorted attenuation of theX-rays from the imaging system 12 for imaging of the subject 14.Moreover, the known component parameters 226 may assist in enhancing aregistration in block 280, such as making it faster by efficiently andmore definitely defining the component for forming the forwardprojection in 250. Moreover, the known component parameters from block226 may further assist in reducing artifacts and distortion due to apredetermined and know effects of the component for the inpainting inblock 310. Thus, the final reconstructed image in block 330 isefficiently and quickly produced based upon the process 200 that may beexecuted with the processing system, such as the image processing unit58 as discussed above.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

In one or more examples, the described techniques may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored as one or more instructions orcode on a computer-readable medium and executed by a hardware-basedprocessing unit. Computer-readable media may include non-transitorycomputer-readable media, which corresponds to a tangible medium such asdata storage media (e.g., RAM, ROM, EEPROM, flash memory, or any othermedium that can be used to store desired program code in the form ofinstructions or data structures and that can be accessed by a computer).

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor” as used herein may refer toany of the foregoing structure or any other physical structure suitablefor implementation of the described techniques. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

What is claimed is:
 1. A method of reducing artifacts in an image due toan object, comprising: accessing parameters of the object; creating atleast one forward projection of the object based on the accessedparameters; registering the object in the forward projection to at leastone acquired projection having the object therein; modifying the atleast one acquired projection to a representation of the registeredobject; and generating a reconstruction based on the modified at leastone acquired projection.
 2. The method of claim 1, wherein modifying theat least one acquired projection includes inpainting the representationof the object in the at least one acquired projection.
 3. The method ofclaim 1, further comprising: acquiring a plurality of the projections;modifying at least a first sub-plurality of acquired projections of theacquired plurality of projections to the representation of theregistered object; wherein generating the reconstruction includesgenerating the reconstruction based on all of at least the firstsub-plurality of acquired projections of the acquired plurality ofprojections.
 4. The method of claim 3, wherein generating thereconstruction based on at least all of the modified first sub-pluralityof acquired projections of the acquired plurality of projectionsincludes generating a three dimensional image.
 5. The method of claim 4,further comprising: generating a visualization of the reconstruction fordisplay with a display device.
 6. The method of claim 5, whereingenerating the visualization comprises at least one of: generating adirect reconstruction of modified projection values of the modifiedfirst sub-plurality of acquired projections; replacing voxels or pixelsthat coincide with the registered object in the modified firstsub-plurality of acquired projections; orienting the visualization suchthat a 2D slice coincides with at least one feature of the object;superimposing a graphical representation of the object on a display ofthe at least one of the projections of the acquired plurality ofprojections; or combinations thereof.
 7. The method of claim 4, whereinthe generated reconstruction is based on at least one of a filtered backprojection, a model-based iterative reconstruction process, orcombinations thereof.
 8. The method of claim 1, further comprising:determining the parameters of the object to include at least one of ageometry, number of portions, dimensions, materials, interaction ofX-rays with the materials, degrees of freedom in motion of the object,or combinations thereof.
 9. The method of claim 8, wherein creating theforward projection of the object based on the accessed parametersincludes creating a digitally reconstructed radiograph of the object.10. The method of claim 8, wherein the determined parameters arecomprised of at least one of exact values based on specifications of theobject, parametrically defined, or combinations thereof.
 11. The methodof claim 10, wherein the parametrically defined parameters of the objectare determined during the registering the object in the forwardprojection to at least one acquired projection having the objecttherein.
 12. The method of claim 1, further comprising: placing theobject in a subject; and acquiring the at least one projection of thesubject and the placed object.
 13. The method of claim 1, whereinmodifying the acquired projections according to the representationcomprises at least one of: an interpolation-based inpainting of theacquired projections; machine-learning based inpainting using priortraining; or determining estimated pixel or voxel values usingpolyenergetic modeling of x-rays in a x-ray beam.
 14. The method ofclaim 1, further comprising: generating a visualization based on thegenerated reconstruction with reduced artifacts in the generatedvisualization due to the objects in the at least one acquired projectionbased on the modified at least one acquired projection.
 15. A system forreducing artifacts in an image due to an object, comprising: a processorsystem configured to execute instructions for: accessing parameters ofthe object; creating at least one forward projection of the object basedon the accessed parameters; registering the object in the forwardprojection to at least one acquired projection having the objecttherein; modifying the at least one acquired projection to arepresentation of the registered object; and generating a reconstructionbased on the modified at least one acquired projection; and a displaydevice to display a visualization based on the generated reconstruction.16. The system of claim 15, wherein the processor system is furtherconfigured for: accessing a plurality of the projections; and modifyingat least a first sub-plurality of acquired projections of the acquiredplurality of projections to the representation of the registered object;wherein generating the reconstruction includes generating thereconstruction based on all of at least the first sub-plurality ofacquired projections of the acquired plurality of projections.
 17. Thesystem of claim 16, wherein generating the reconstruction based on atleast all of the modified first sub-plurality of acquired projections ofthe acquired plurality of projections includes generating a threedimensional image.
 18. The system of claim 17, wherein the processorsystem is further configured for: generating the visualization fordisplay with the display device comprising at least one of: generating adirect reconstruction of modified projection values of the modifiedfirst sub-plurality of acquired projections; replacing voxels thatcoincide with the registered object in the modified first sub-pluralityof acquired projections; or orienting the visualization such that a 2Dslice coincides with at least one feature of the object; superimposing agraphical representation of the object on a display of the at least oneof the projections of the acquired plurality of projections; orcombinations thereof.
 19. The system of claim 15, wherein the processorsystem is further configured for: determining the parameters of theobject to include at least one of a geometry, number of portions,dimensions, materials, interaction of X-rays with the materials, degreesof freedom in motion of the object, or combinations thereof.
 20. Amethod of reducing artifacts in an image due to an object, comprising:operating a processor system for: accessing parameters of the object;creating at least one forward projection of the object based on theaccessed parameters; registering the object in the forward projection toat least one acquired projection having the object therein; modifyingthe at least one acquired projection to a representation of theregistered object; and generating a reconstruction based on the modifiedat least one acquired projection; displaying a visualization of thegenerated reconstruction.